Falling into water from great height?

[Mokele]

So, I'm sure we've all seen plenty of movies where, in order to escape some enemy, Our Intrepid Hero jumps off something really tall into water below.

 

I also recall hearing the urban legend that hitting the water from more than 90 feet up is like hitting concrete. This is obviously wrong, since the world record high dive is almost twice that (172 feet, Dana Kunze).

 

So, what is the actual maximum height, and if nobody knows, how would it be best to calculate it, based on force, energy change, or impulse?

 

Mokele

[MolecularEnergy]

I think, its impossible to tell what is fatal, or atleast, usually fatal. If someone can fall at 172 feet, i would have thought it be enough for a maximal acceleration down to earth due to the gravitational field... Maybe i am wrong?

[swansont]

How you hit the water matters.

 

At some point you hit terminal velocity, and additional height means nothing.

[Mokele]

I was just looking it up, and apparently to hit terminal velocity in arms-in position (the most streamlined), you'd need to jump from a bit more than 400 meters. With legs and arms spread, you'd need to jump from 154 meters, which is still about 3 times to record.

 

How you hit *is* important, but for the sake of argument, let's assume they orient their body vertically, arms and legs tucked in, feet first. This should allow for more streamlined entry, but also mean that your legs could absorb some of the damage (since, after all, you don't actually *need* your legs to live). Plus, many of your internal organs are structured to hang via connective tissue and attachment structures, so this would mean their deceleration would push them up (which has less risk of rupturing valuable connections). I'd be a bit worried about the celiac, superior and inferior messenteric arteries, though. Still, there's a lot of messentery to distribute stress through.

 

Mokele

[iNow]

It also differs whether or not the water is turbulent. Much easier to dive into water that is moving/turbulent than still (due to surface tension issues I presume).

[swansont]

I recall reading about Alcides Moreno, who survived a 47-story fall from a skyscraper, and the information that survivability. I thought the probability of surviving flattened at about 10 stories.

[Mokele]

I just dug up the following two links:

 

Survival of 15% from a 59 meter fall off a bridge (however, subjects were suicidal, so may not have tried things like adopting a good posture).

 

Survival of high-velocity free-falls into the water - notes that 116 ft/sec is survivable, equivalent to a 186 foot fall. Apparently, feet first entries are the only people to ever survive without injuries, and cliff divers regularly dive 100-135 feet.

 

Mokele

[npts2020]

I just dug up the following two links:

 

Survival of 15% from a 59 meter fall off a bridge (however, subjects were suicidal, so may not have tried things like adopting a good posture).

 

Survival of high-velocity free-falls into the water - notes that 116 ft/sec is survivable, equivalent to a 186 foot fall. Apparently, feet first entries are the only people to ever survive without injuries, and cliff divers regularly dive 100-135 feet.

 

Mokele

 

Feet first with arms and legs crossed and toes pointed downward. I have done this from at least 25 meters (once). Finishing the plunge was rather exhilirating but I wouldn't recommend doing it for entertainment.